The field of disclosure relates to coatings that inhibit the formation and adhesion of deposits on surfaces of hydrocarbon fuel contacting components. More specifically, to methods for manufacturing an additively manufactured hydrocarbon fuel contacting component that reduces the deposition of carbonaceous deposits on the surfaces of fuel contacting components, such as, but not limited to fuel nozzles, swirlers, and other fuel system components of gas turbine engines that are manufactured by additive manufacturing.
Additive manufacturing is a known technology that enables the “3D-printing” of components of various materials including metals and plastics. In additive manufacturing, a part is built in a layer-by-layer manner by leveling metal powder and selectively fusing the powder using a high-power laser. After each layer, more powder is added and the laser forms the next layer, simultaneously fusing it to the prior layers to fabricate a complete component buried in a powder bed. When removed from the powder bed, the component typically has a rough surface finish that must be improved via post-build processes such as grit blasting, grinding, sanding, or polishing to meet industry standards. Furthermore, the surfaces internal passages for liquid hydrocarbon fuel contacting components require additional processing to protect the component surface from the harsh operating environment of gas turbine engines.
In order to increase the efficiency of gas turbine engines, higher operating temperatures are sought. For this reason, the high temperature durability of the engine components must correspondingly increase. With the formulation of superalloys, such as nickel-based and cobalt-based, significant advances in high-temperature capabilities are being achieved. Consequently, in the absence of a protective coating, sensitive superalloy components, e.g., the turbine and combustor, typically will not endure long service exposures without accelerated wear. One such coating is referred to as a coke barrier coating to prevent the formation of undesired carbonaceous deposits on fuel contacting components that occur when hydrocarbon fluids, such as fuels and lubricating oils, are at elevated temperatures.
In the case of fuels, it is generally accepted that there are two distinct mechanisms occurring within two overlapping temperature ranges. In the first mechanism, referred to as the coking process, a generally consistent increase in the rate of formation of carbonaceous coke deposits occurs above temperatures of about 650 degrees Fahrenheit (° F.) (345 degrees Celsius (° C.)). Coke formation is the result of high levels of hydrocarbon pyrolysis, and eventually limits the usefulness of the fuel contacting component. A second mechanism primarily occurs at lower temperatures, generally in the range of about 220° F. to about 650° F. (about 105° C. to about 345° C.), and involves oxidation reactions that lead to polymerization and carbonaceous gum deposits. Both coke and gum formation and deposits can occur simultaneously at temperatures where the above ranges overlap. Moreover, the rough surface finish of additively manufactured components generally includes a number of troughs or pits that allow fuel to pool therein, leading to coke and gum formation that subsequently prevent efficient flow of the fuel through the engine.
Higher engine operation temperatures and the rough interior surface finishes increase the likelihood that carbonaceous deposits can severely choke the flow of fuel and air through fuel nozzles and swirlers, affecting operating conditions (e.g., mixing of fuel and air, proper flow of fuel and oxygen into the combustor) and may reduce fuel efficiency and increase emissions. As a result it is important to reduce the rough interior finish and protect the fuel contacting surfaces of these components with a coating that prevents the formation and adhesion of both coke and gum deposits.